Modern power electronic device is an essential part of a device applied in the industries of modern electric power, electronics, electric motors and energy sources. The power conversion efficiency of the power electronic device is always an important goal pursued, which can also be represented by a loss of the device.
A power semiconductor device is a core component of a modern power electronic device, the loss of the power semiconductor device is the most important constituent part of the loss of the modern power electronic device, and the performance of the power semiconductor device directly determines the reliability and conversion efficiency of the power electronic device. In order to design a power electronic device with higher performance, a power semiconductor device with a low power loss is desired.
A power switch circuit, of various circuit topologies are employed in modern power electronic devices according to various practical operation conditions, such as a Buck circuit, a Boost circuit, a half-bridge circuit, a diode-clamping three-level circuit, a T-Type three-level circuit, etc., which are commonly used. It is well known for those skilled in the art that a power switch circuit typically includes at least one switch and one controller, wherein power conversion, such as conversion between DC and DC or conversion between DC and AC, can be achieved by turning on and turning off the switch under control signal of the controller.
The switch of the power switch circuit with the above described circuit typically operates in an on state or an off state, and the loss of the switch is mainly consisted of two parts: a conduction loss and a switching loss. When the switch is in an on state, the current flowing through the switch causes the conduction loss; when the switch is being switched from the on-state to the off-state, or switched from the on-state to the off-state, the switching loss of the device will be generated. The switching loss can be further divided into: a turning-off loss generated during the switching from the on-state to the off-state, and a turning-on loss generated during the switching from the off-state to the on-state.
In practical operation, the turning-on loss is related to the switch itself, the parasitic inductance, and the reverse recovery charge of the fly-wheel diode. The turning-off loss is related to the switch itself and the parasitic inductance, but is less related to the forward turning-on of the fly-wheel diode.
Take the Buck circuit as an example. The Buck circuit in the related art is illustrated in FIG. 1, including a switch 1-1, a fly-wheel diode D, an parasitic inductor Ls connected in series with the switch 1-1, an input Voltage Vin, an input capacitor Cdc, an output filtering inductor Lo and an output load (Load). The conversion of power supply is achieved by controlling the turning on and turning off of the switch 1-1. The input voltage Vin of the Buck circuit is connected in parallel with the input capacitor Cdc and has a positive voltage terminal P and a negative voltage terminal N. The branch of the switch 1-1 and the parasitic inductor Ls connected in series is connected to a positive voltage terminal P, the fly-wheel diode D is connected to a negative voltage terminal N, and a midpoint between the switch 1-1 and the fly-wheel diode D is connected with the output filtering inductor Lo and the output load (Load).
The switch 1-1 can operates in an on state or an off state through control of a gate G.
When the switch 1-1 is turned on, a current flows from an input terminal and the input capacitor Cdc to the output filtering inductor Lo and the output load (Load) through the switch 1-1, thus the turning-on loss is generated in the switch 1-1. The parasitic inductor Ls can slow down the rate of change of the turning on current in the switch 1-1 and make the change of current lag to be behind the change of voltage, reduce the time period during which the changed current is overlapped with the changed voltage, and decrease the turning-on loss of the power switch device, but will also reduce the speed of turning on. On the other hand, the parasitic inductor Ls will reduce the rate of change of current in the reverse recovery process, and cause a lower reverse current and reduce the reverse recovery loss. Thus, increasing the inductance value of the parasitic inductor Ls can reduce the turning-on loss.
When the switch 1-1 is turned off, the current flowing through the switch 1-1 is blocked. In the current of the output filtering inductor Lo and the output load (Load), the current flowing through the parasitic inductor Ls and the switch 1-1 is reduced and the forward current of the fly-wheel diode D is increased. The turning-off loss of the switch 1-1 is generated in this process. The parasitic inductor Ls can slow down the rate of change of the turning off current in the switch 1-1, prolong the time period during which the changed current is overlapped with the changed voltage, and increase the turning-off loss of the power switch device.
Thus, the effect of the parasitic inductor on the loss can be described as follows: in the process of turning on the switch, the parasitic inductor will reduce the turning-on loss; and in the process of turning off the switch, the parasitic inductor will increase the turning-off loss.
Conventionally, the method for reducing the loss of the power semiconductor device includes:
1. Designing a suitable parasitic inductor, taking both of the turning-on loss and the turning-off loss into account. However this method cannot achieve both of a minimum turning-on loss and a minimum turning-off loss.
2. Employing a soft switching circuit, through which the turning-on loss or the turning-off loss of the power switch device can be reduced. However an additional soft switching circuit is typically required.
3. Employing semiconductor material with higher performance, such as a new generation wide band-gap device, which can reduce the loss of semiconductor device. However this method typically causes an increased cost of the semiconductor device.